Polarizing plate and image display apparatus comprising same

ABSTRACT

The present invention relates to a polarizing plate including: a polarizer; and a protective layer formed on at least one surface of the polarizer, in which the protective layer is a cured product of a radical curable composition including: (A) a radical polymerizable compound including at least one hydrophilic functional group in a molecule thereof; (B) a multifunctional (meth)acrylic compound; (C) a phosphate compound including one or two (meth)acryl groups in a molecule thereof; and (D) a radical initiator, and an image display device including the same.

TECHNICAL FIELD

The present invention relates to a polarizing plate and an image displaydevice including the same, and more specifically, to a polarizing platewhich has excellent adhesion between a polarizer and a protective layer,is excellent in water resistance, and may be manufactured as athin-type, and an image display device including the same.

BACKGROUND ART

A polarizing plate has been usually used in a structure, in which aprotective film is stacked on both surfaces of a polarizer formed of apolyvinyl alcohol (hereinafter, referred to as ‘PVA’)-based resin dyedwith a dichroic dye or iodine. In this case, a triacetyl cellulose(TAC)-based film has been frequently used as the protective film becausethe film is excellent in optical transparency or moisture permeability.

Meanwhile, as a liquid crystal display device has recently beendeveloped into a mobile device such as a laptop personal computer, acellular phone and a car navigation system, it is required that apolarizing plate which constitutes a liquid crystal display device isthin and light weight. However, in a polarizing plate in which a TACfilm and the like are laminated as the protective film as describedabove, it is difficult to maintain a thickness of the protective film at20 μm or less from the viewpoint of handling property or durabilityperformance during the operation, so that there is a limitation for theliquid crystal device to be thin and light weight.

In order to solve the aforementioned problems, a technology has beensuggested, in which a protective film is provided on only one surface ofa polarizer, and a transparent thin film layer is formed by coating anactive energy ray curable composition on the other surface thereof.Meanwhile, the active energy ray curable composition which has beensuggested may be classified into a radical curable composition and acationic curable composition according to the curing method. In thiscase, when a transparent thin film layer is formed using a cationiccurable composition, there is an advantage in that excellent adhesionwith the polarizer is achieved, but there are many disadvantages in themanufacturing process due to a slow curing rate and a low degree ofcuring.

In order to solve such problems of the cationic curable composition, atechnology has been suggested, in which a transparent thin film layer isformed by using a radical curable composition which includes an acrylicor acryl amide-based compound as a main component. However, in the caseof a radical curable composition including an acrylic oracrylamide-based compound as a main component, there are problems inthat the curing rate is fast compared to a cationic curable composition,but the curing rate becomes slow under a high humidity atmosphere, andwater resistance is not good such that a transparent protective layerformed by using the same does not have sufficient adhesion with apolarizer, and iodide ions in the polarizer are affected.

Therefore, there is a need for a new polarizing plate, which isexcellent in adhesion between a polarizer and a protective layer, and isexcellent in water resistance while having a thin protective layer whichmay be formed by curing radicals.

DISCLOSURE Technical Problem

The present invention has been made in an effort to solve theaforementioned problem and provide a polarizing plate, which hasexcellent adhesion between a polarizer and a protective layer and isexcellent in water resistance, and may be manufactured as a thin-type,and an image display device including the same.

Technical Solution

In one aspect, the present invention provides a polarizing plateincluding: a polarizer; and a protective layer formed on at least onesurface of the polarizer, in which the protective layer is a curedproduct of a radical curable composition including: (A) a radicalpolymerizable compound having at least one hydrophilic functional groupin a molecule thereof; (B) a multifunctional (meth)acrylic compound; (C)a phosphate compound having one or two (meth)acryl groups in a moleculethereof; and (D) a radical initiator.

In this case, it is preferred that the radical curable compositionincludes more than 30 parts by weight and 93 parts by weight or less of(A) the radical polymerizable compound having at least one hydrophilicfunctional group in a molecule thereof; 5 to 40 parts by weight of (B)the multifunctional (meth)acrylic compound; 1 to 40 parts by weight of(C) the phosphate compound including one or two (meth)acryl groups in amolecule thereof; and (D) 0.5 to 20 parts by weight of the radicalinitiator, based on 100 parts by weight of the radical curablecomposition.

Further, it is preferred that the radical curable composition has atotal hydroxyl value of 500 to 900 mg KOH/g.

Meanwhile, the hydrophilic functional group of (A) the radical curablecomposition is preferably a hydroxy group.

Meanwhile, it is more preferred that as (A) the radical polymerizablecompound, a mixture of (a-1) a radical polymerizable compound having onehydroxy group in a molecule thereof and (a-2) a radical polymerizablecompound having at least two hydroxy groups in a molecule thereof isused.

In addition, it is preferred that (b) the radical polymerizable compoundhas an acid value of 100 to 1,000 mg·KOH/g.

Meanwhile, it is preferred that (B) the multifunctional (meth)acryliccompound includes one or more selected from the group consisting ofcompounds represented by the following [Formula I] to [Formula III].

In [Formula I], R₁ and R₂ are each independently a (meth)acryloyloxygroup or a (meth)acryloyloxy alkyl group.

In [Formula II], R₃, R₄ and R₅ are each independently a(meth)acryloyloxy group, or a (meth)acryloyloxy alkyl group, and R₆ is a(meth)acryloyloxy group, a (meth)acryloyloxy alkyl group, a hydroxygroup, or a substituted or unsubstituted C_(1˜10) alkyl group.

In [Formula III], R₇ is a substituted or unsubstituted C_(1˜10)alkylene, and R₈ and R₉ are each independently a (meth)acryloyloxy groupor a (meth)acryloyloxy alkyl group.

Meanwhile, it is preferred that (C) the phosphate compound includes acompound represented by the following [Formula IV].

In [Formula IV], R₁₀ is a substituted or unsubstituted C_(1˜10) alkylenegroup, a substituted or unsubstituted C_(4˜14) cycloalkylene group, asubstituted or unsubstituted C_(6˜14) arylene group, or a combinationthereof; R₁₁ is hydrogen or a methyl group; and n is an integer of 1 and2, m is an integer of 1 and 2, and n+m=3.

Meanwhile, it is preferred that the protective layer has a thickness of0.5 to 20 μm.

Meanwhile, in the polarizing plate of the present invention, aprotective film may be further attached to a surface opposite to asurface of the polarizer, on which a protective layer is formed, throughan adhesive layer.

Furthermore, the polarizing plate of the present invention may furtherinclude an adhesion layer at the upper portion of the protective layer.

In another aspect, the present invention provides an image displaydevice including the polarizing plate.

Advantageous Effects

The polarizing plate of the present invention has excellent adhesionbetween a polarizer and a protective layer, and is excellent in waterresistance such that discoloration of iodide ions in the polarizer maybe prevented even under a high humidity environment. Further, thepolarizing plate of the present invention has a protective layer havinga small thickness as compared to a polarizing plate having a transparentprotective film in the related art, and thus may be manufactured as athin-type.

MODE FOR INVENTION

Hereinafter, preferred exemplary embodiments of the present inventionwill be described. However, the exemplary embodiments of the presentinvention may be modified in various forms, and the scope of the presentinvention is not limited to the exemplary embodiments which will bedescribed below. Further, exemplary embodiments of the present inventionare provided to more completely explain the present invention to aperson with ordinary skill in the art.

1. Polarizing Plate

As a result of repeated studies, the present inventors have found thatwhen a multifunctional (meth)acrylic compound is used in mixture with aphosphate compound having one or two (meth)acryl groups in a moleculethereof in a radical curable composition having a hydrophilic functionalgroup for forming a protective layer, adhesion and water resistance areexcellent, thereby completing the present invention.

More specifically, the present invention is a polarizing plateincluding: a polarizer; and a protective layer formed on at least onesurface of the polarizer, in which the protective layer is a curedproduct of a radical curable composition including: (A) a radicalpolymerizable compound having at least one hydrophilic functional groupin a molecule thereof; (B) a multifunctional (meth)acrylic compound; (C)a phosphate compound having one or two (meth)acryl groups in a moleculethereof; and (D) a radical initiator.

1-1. Polarizer

First, as the polarizer of the present invention, it is possible to usea polarizer well known in the art, for example, a film composed ofpolyvinyl alcohol (PVA) including iodine or a dichroic dye. Thepolarizer may be manufactured by dyeing iodine or a dichromatic dye tothe PVA film, but the manufacturing method thereof is not particularlylimited. In the present specification, the polarizer refers to a statein which the polarizer does not include a protective layer (or aprotective film), and the polarizing plate refers to a state in whichthe polarizing plate includes a polarizer and a protective layer (or aprotective film).

Meanwhile, when the polarizer is a polyvinyl alcohol-based film, thepolyvinyl alcohol-based film may be used without particular limitationas long as the film includes a polyvinyl alcohol resin or a derivativethereof. In this case, examples of the derivative of the polyvinylalcohol resin include, but are not limited to, a polyvinyl formal resin,a polyvinyl acetal resin and the like. Also, as the polyvinylalcohol-based film, it is also possible to use a commercially availablepolyvinyl alcohol-based film generally used in the manufacture of apolarizer in the art, for example, P30, PE30 and PE60 manufactured byKuraray Co., Ltd., and M3000 and M6000 manufactured by Nippon SyntheticChemical Industry Co., Ltd., and the like.

Meanwhile, the degree of polymerization of the polyvinyl alcohol-basedfilm may be in a range of 1,000 to 10,000, preferably, in a range of1,500 to 5,000, but is not limited thereto. This is because when thedegree of polymerization satisfies the range, molecules freely move, andmay be flexibly mixed with iodine or a dichroic dye, and the like.

1-2. Protective Layer

Next, the protective layer of the present invention is formed by usingthe radical curable composition in order to support and protect apolarizer, and may be formed by a method well known in the art. Forexample, the protective layer may be formed by a method of applying theradical curable composition on one surface of a polarizer to form aprotective layer by a coating method well known in the art, for example,a methods such as spin coating, bar coating, roll coating, gravurecoating and blade coating, and then curing the protective layer throughirradiation of an active energy ray. The method of irradiating an activeenergy ray is not particularly limited, and for example, may beperformed by irradiating UV light at 10 to about 2,500 mJ/cm² using a UVlight irradiation device (fusion lamp, D bulb).

In this case, the radical curable composition of the present inventionincludes: (A) the radical polymerizable compound having at least onehydrophilic functional group in a molecule thereof; (B) themultifunctional (meth)acrylic compound; (C) the phosphate compoundincluding one or two (meth)acryl groups in a molecule thereof; and (D)the radical initiator.

More preferably, the radical curable composition of the presentinvention includes more than 30 parts by weight and 93 parts by weightor less of (A) the radical polymerizable compound including at least onehydrophilic functional group in a molecule thereof; 5 to 40 parts byweight of (B) the multifunctional (meth)acrylic compound; 1 to 40 partsby weight of (C) the phosphate compound including one or two (meth)acrylgroups in a molecule thereof; and (D) 0.5 to 20 parts by weight of theradical initiator, based on 100 parts by weight of the radical curablecomposition.

A. (A) Radical Polymerizable Compound

First, the radical polymerizable compound included in the radicalcurable composition according to the present invention is a componentfor implementing adhesion between a polarizer and a protective layer,may have at least one hydrophilic functional group in a molecule thereofto implement adhesion through a hydrogen bond, and may also be usedwithout particular limitation as long as the radical polymerizablecompound may achieve the radical polymerization due to the presence ofan unsaturated double bond between carbons in a molecule thereof. Inthis case, the hydrophilic functional group is not particularly limitedas long as the hydrophilic functional group may obtain a hydrogen bond,such as a hydroxy group, a carboxyl group, a urethane group, an aminegroup, and an amide group, but among them, particularly, a hydroxy groupor a carboxyl group is more preferred for implementing excellentadhesion.

More specifically, (A) the radical polymerizable compound may be, but isnot limited to, for example, a compound represented by the following[Formula 1] to [Formula 24]. These may be used either alone or in amixture.

Meanwhile, the radical polymerizable compound is not limited thereto,but it is preferred to use particularly a mixture of (a-1) a radicalpolymerizable compound having at least one hydroxy group in a moleculethereof (for example, [Formula 1] to [Formula 6] and the like) and (a-2)a radical polymer having at least two hydroxy groups in a moleculethereof (for example, [Formula 7] to [Formula 24] and the like) amongthem in terms of implementing excellent adhesion and securing heatresistance.

Meanwhile, the content of the radical polymerizable compound of thepresent invention may be more than 30 parts by weight to 93 parts byweight or less, preferably 35 to 90 parts by weight, and more preferably45 to 90 parts by weight, based on 100 parts by weight of the radicalcurable composition. This is because when the radical polymerizablecompound is included in such content, excellent adhesion may beimplemented.

B. (B) Multifunctional (Meth)Acrylic Compound

Next, the multifunctional (meth)acrylic compound included in the radicalcurable composition according to the present invention is a componentfor increasing the degree of crosslinking in the protective layer toimprove water resistance and exhibit stable physical properties even ina high humidity environment, and it is possible to use variousmultifunctional (meth)acrylic compound widely known in the art withoutparticular limitation. However, in the present specification, except forthe following multifunctional (meth)acrylic compounds enumerated as anexample, a compound corresponding to the above-described (A) compoundand (E) a compound to be described below is excluded from themultifunctional (meth)acrylic compounds.

In the present invention, examples of the multifunctional (meth)acryliccompound include ethylene glycol di(meth)acrylate, 1,3-butanedioldi(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanedioldi(meth)acrylate, 1,9-nonanediol di(meth)acrylate, neopentyl glycoldi(meth)acrylate, trimethylol propane di(meth)acrylate, pentaerythritoldi(meth)acrylate, ditrimethylol propane di(meth)acrylate, diethyleneglycol di(meth)acrylate, triethylene glycol di(meth)acrylate,dipropylene glycol di(meth)acrylate, tripropylene glycoldi(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropyleneglycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate,silicone di(meth)acrylate, hydroxypivalic acid ester neopentyl glycoldi(meth)acrylate, 2,2-bis[4-(meth)acryloyloxyethoxyethoxyphenyl]propane,2,2-bis[4-(meth)acryloyloxyethoxyethoxycyclohexyl]propane, hydrogenateddicyclopentadienyl di(meth)acrylate, tricyclodecane dimethaneoldi(meth)acrylate, 1,3-dioxane-2,5-diyl di(meth)acrylate,di(meth)acrylate of2-(2-hydroxy-1,1-dimethylethyl)-5-ethyl-5-hydroxymethyl-1,3-dioxane,tris(hydroxyethyl)isocyanurate di(meth)acrylate, glycerintri(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethyolpropane tri(meth)acrylate, di trimethylol propanetetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritoltetra(meth)acrylate, di pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, di pentaerythritol hexa(meth)acrylate and the like. These may be used either alone or in amixture.

Meanwhile, the multifunctional (meth)acrylic compound is more preferablyone or more selected from the group consisting of compounds representedby the following [Formula I] to [Formula III], but is not limitedthereto. This is because water resistance improvement effects are stillexcellent.

In [Formula I], R₁ and R₂ are each independently a (meth)acryloyloxygroup or a (meth)acryloyloxy alkyl group.

In this case, in R₁ and R₂, the alkyl of the (meth)acryloyloxy alkylgroup refers to a straight-chained or branch-chained hydrocarbon moietyhaving 1 to 10, or 1 to 8, or 1 to 4 carbon atoms, and the(meth)acryloyloxy group may be substituted at any position of the alkylgroup. The remaining one or more hydrogen atoms included in the alkylmay be substituted with any substituent.

In [Formula II], R₃, R₄ and R₅ are each independently a(meth)acryloyloxy group, or a (meth)acryloyloxy alkyl group, and R₆ is a(meth)acryloyloxy group, a (meth)acryloyloxy alkyl group, a hydroxygroup, or a substituted or unsubstituted C₁₋₁₀ alkyl group.

In this case, in R₃, R₄, R₅ and R₆, the alkyl of the (meth)acryloyloxyalkyl group refers to a straight-chained or branch-chained hydrocarbonmoiety having 1 to 10, or 1 to 8, or 1 to 4 carbon atoms, and the(meth)acryloyloxy group may be substituted at any position of the alkylgroup. The remaining one or more hydrogen atoms included in the alkylmay be substituted with any substituent.

Further, in R₆, the alkyl group refers to a straight-chained orbranch-chained hydrocarbon moiety having 1 to 10, or 1 to 8, or 1 to 4carbon atoms, and one or more hydrogen atoms included in the alkyl groupmay be substituted with any substituent.

In [Formula III], R₇ is a substituted or unsubstituted C_(1˜10)alkylene, and R₈ and R₉ are each independently a (meth)acryloyloxy groupor a (meth)acryloyloxy alkyl group.

In this case, in R₇, the alkylene refers to a straight-chained orbranch-chained divalent hydrocarbon moiety having 1 to 10, or 1 to 8, or1 to 6 carbon atoms, and the alkylene group in the present specificationmay also include at least one unsaturated bond in a molecule thereof.Meanwhile, examples of the alkylene group include, but are not limitedto, methylene, ethylene, trimethylene, tetramethylene, pentamethylene,hexamethylene, heptamethylene, nonamethylene, decamethylene and thelike. One or more hydrogen atoms included in the alkylene may besubstituted with any substituent.

Furthermore, in R₈ and R₉, the alkyl of the (meth)acryloyloxy alkylgroup refers to a straight-chained or branch-chained hydrocarbon moietyhaving 1 to 10, or 1 to 8, or 1 to 4 carbon atoms, and the(meth)acryloyloxy group may be substituted at any position of the alkylgroup. The remaining one or more hydrogen atoms included in the alkylmay be substituted with any substituent.

More specifically, (B) the multifunctional (meth)acrylic compound isparticularly preferably one or more selected from the group consistingof compounds represented by the following [Formula 25] to [Formula 28],but is not limited thereto.

Meanwhile, the content of the multifunctional (meth)acrylic compound ofthe present invention may be 5 to 40 parts by weight, preferably 5 to 35parts by weight, and more preferably 5 to 30 parts by weight, based on100 parts by weight of the radical curable composition. When the contentof the multifunctional (meth)acrylic compound is more than the range,adhesion may not be sufficient, and when the content is less than therange, water resistance may be reduced.

C. (C) Phosphate Compound

Next, the phosphate compound included in the radical curable compositionaccording to the present invention is a component for further enhancingadhesion and water resistance of the protective layer, and it ispossible to use various phosphate compounds including one or two(meth)acryl groups in a molecule thereof. According to the study resultsof the present inventors of the present invention, it is difficult tosecure sufficient adhesion and water resistance only by adding themultifunctional (meth)acrylic compound, and only when the phosphatecompound including one or two (meth)acryl groups in a molecule thereofand the multifunctional (meth)acrylic compound are simultaneously added,it is possible manufacture a protective layer which satisfies bothexcellent adhesion and water resistance.

Meanwhile, the phosphate compound is not limited to, but is morepreferably a compound represented by the following [Formula V]. This isbecause an effect of enhancing adhesion and water resistance isparticularly excellent.

In [Formula IV], R₁₀ is a substituted or unsubstituted C_(1˜10) alkylenegroup, a substituted or unsubstituted C_(4˜14) cycloalkylene group, asubstituted or unsubstituted C_(6˜14) arylene group, or a combinationthereof; R₁₁ is hydrogen or a methyl group; and n is an integer of 1 and2, m is an integer of 1 and 2, and n+m=3.

In this case, in R₁₀, the alkylene group refers to a straight-chained orbranch-chained divalent hydrocarbon moiety having 1 to 10, or 1 to 8, or1 to 4 carbon atoms, and the alkylene group in the present specificationmay also include at least one unsaturated bond in a molecule thereof.Meanwhile, examples of the alkylene group include, but are not limitedto, methylene, ethylene, trimethylene, tetramethylene, pentamethylene,hexamethylene, heptamethylene, nonamethylene, decamethylene and thelike. One or more hydrogen atoms included in the alkylene group may besubstituted with any substituent.

In addition, in R₁₀, the cycloalkylene group refers to a non-aromaticdivalent monocyclic, bicyclic or tricyclic hydrocarbon moiety of 4 to14, or 4 to 10, or 4 to 6 ring carbons, and the alkylene group in thepresent specification may also include at least one unsaturated bond ina molecule thereof. Meanwhile, examples of the cycloalkylene groupinclude, but are not limited to, a divalent cyclopentane ring, adivalent cyclohexane ring and the like. One or more hydrogen atomsincluded in the cycloalkylene group may be substituted with anysubstituent.

Furthermore, in R₁₀, the arylene group refers to a divalent monocyclic,bicyclic or tricyclic aromatic hydrocarbon moiety having 6 to 14, or 6to 12 ring atoms, and examples thereof include, but are not limited to,a divalent benzene ring, a divalent naphthalene ring, a divalentanthracene ring, a divalent biphenyl ring and the like. One or morehydrogen atoms included in the arylene group may be substituted with anysubstituent.

Meanwhile, R₁₀ is not limited thereto, but among them, is preferably asubstituted or unsubstituted C_(1˜10) alkylene group, more preferably asubstituted or unsubstituted C_(1˜8) alkylene group, and even morepreferably a substituted or unsubstituted C_(1˜4) alkylene group.

More specifically, the phosphate compound is particularly preferably oneor more selected from the group consisting of compounds represented bythe following [Formula 29] to [Formula 32], but is not limited thereto.

Meanwhile, the content of the phosphate compound of the presentinvention may be 1 to 40 parts by weight, preferably 1 to 35 parts byweight, and more preferably 1 to 30 parts by weight, based on 100 partsby weight of the radical curable composition. When the content of thephosphate compound is more than the range, adhesion and the glasstransition temperature may be reduced, and when the content is less thanthe range, water resistance may be reduced.

D. (D) Radical Initiator

Next, the radical initiator included in the radical curable compositionaccording to the present invention is for promoting radicalpolymerizability to enhance the curing rate. In this case, as theradical initiator, radical initiators generally used in the art may beused without limitation, and the radical initiator may be, for example,one or more selected from the group consisting of1-hydroxy-cyclohexyl-phenyl-ketone,2-hydroxy-2-methyl-1-phenyl-1-propanone,2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone,methylbenzoylformate, oxy-phenyl-acetic acid-2-[2oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester, oxy-phenyl-aceticacid-2-[2-hydroxy-ethoxy]-ethyl ester,alpha-dimethoxy-alpha-phenylacetophenone,2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone,2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone,diphenyl (2,4,6-trimethylbenzoyl)-phosphine oxide, andphenylbis(2,4,6-trimethylbenzoyl)-phosphineoxide. Particularly in thepresent invention, the radical initiator is preferablyphenylbis(2,4,6-trimethylbenzoyl)-phosphineoxide.

Meanwhile, it is preferred that (C) the content of the radical initiatoris 0.5 to 20 parts by weight, 0.5 to 15 parts by weight, or 0.5 to 10parts by weight, based on 100 parts by weight of the radical curablecomposition. This is because when the content of the radical initiatorsatisfies the numerical range, the protective layer may be smoothlycured.

E. Physical Properties of Composition

Meanwhile, the aforementioned radical curable composition of the presentinvention has a total hydroxyl value of 500 to 900 mg·KOH/g, morepreferably 500 to 850 mg·KOH/g, and even more preferably 500 to 800mg·KOH/g. When the hydroxyl value of the radical curable compositionsatisfies the numerical range as described above, there is an advantagein that a protective layer formed by using the composition may stablymaintain high adhesion with a polarizer even under a relatively highhumidity condition, and there is also an advantage in that the bondingstrength inside an adhesive cured is so strong that the protective layerhas a high glass transition temperature, and accordingly, thermalstability may be secured.

Meanwhile, the hydroxyl value refers to the number of mg of potassiumhydroxide (KOH) required to neutralize acetic acid bonded to a hydroxygroup when 1 g of a sample is acetylated, and the measurement method isnot particularly limited. For example, the hydroxyl value in a samplemay be calculated through the following Equation (1).

(molecular weight of KOH×number of —OH in a sample×1,000)/molecularweight of the sample  Equation (1):

Furthermore, the glass transition temperature of the radical curablecomposition after curing is 50° C. or more, and may be, for example, 80°C. to 300° C., or 90° C. to 200° C. When the radical curable compositionhas a glass transition temperature in the numerical range as describedabove, the protective layer may have excellent heat resistance and waterresistance.

Further, it is preferred that the radical curable composition has aviscosity of 10 to 300 cP or 20 to 100 cP. When the viscosity of thecomposition satisfies the numerical range, there is an advantage in thatworkability is excellent because the protective layer may be thinlyformed, and has a low viscosity.

Meanwhile, the thickness of a protective layer formed by using theradical curable composition is preferably 0.5 to 20 μm, and may be, forexample, 0.5 to 15 μm or 0.5 to 10 μm. This is because a polarizingplate manufactured may become thin and light weight when the thicknessof the protective layer satisfies the range. When the thickness is lessthan 0.5 μm, thermal impact stability and curl characteristics of thepolarizer are vulnerable, and when the thickness is 20 μm or more, it isdifficult to make the polarizing plate thin and light weight.

1-3. Protective Film

Meanwhile, the polarizing plate of the present invention may furtherinclude a protective film on one surface of the polarizer, if necessary.More specifically, when the protective layer is formed on one surface ofthe polarizer in the polarizing plate of the present invention, aseparate protective film may be attached to a surface opposite to thesurface, on which a protective layer is formed, through an adhesivelayer in order to support and protect the polarizer.

In this case, the protective film is provided for supporting andprotecting a polarizer, and it is possible to use protective filmsformed of various materials generally known in the art, for example, acellulose-based film, a polyethylene terephthalate (PET) film, acycloolefin polymer (COP) film, an acrylic film and the like withoutlimitation. Among them, it is particularly preferred that an acrylicfilm is used in consideration of optical properties, durability,economic efficiency and the like.

Meanwhile, the acrylic film which may be used in the present inventionmay be obtained by molding a molding material including a(meth)acrylate-based resin as a main component by extrusion molding. Inthis case, the (meth)acrylate-based resin includes a resin including a(meth)acrylate-based unit as a main component, and is a concept whichincludes not only a homopolymer resin composed of a (meth)acrylate-basedunit but also a copolymer resin in which other monomer units other thanthe (meth)acrylate-based unit are copolymerized, and a blend resin inwhich other resins are blended with the aforementioned(meth)acrylate-based resin.

Meanwhile, the (meth)acrylate-based unit may be, for example, analkyl(meth)acrylate-based unit. Here, the alkyl(meth)acrylate-based unitrefers to both an alkyl acrylate-based unit and an alkylmethacrylate-based unit, and the alkyl group of thealkyl(meth)acrylate-based unit has preferably 1 to 10 carbon atoms, andmore preferably 1 to 4 carbon atoms.

Further, examples of a monomer unit capable of being copolymerized withthe (meth)acrylate-based unit include a styrene-based unit, a maleicanhydride-based unit, a maleimide-based unit and the like. In this case,examples of the styrene-based unit include, but are not limited to,styrene, α-methylstyrene and the like; examples of the maleicanhydride-based monomer include, but are not limited to, maleicanhydride, methyl maleic anhydride, cyclohexyl maleic anhydride, phenylmaleic anhydride, and the like; and examples of the maleimide-basedmonomer include, but are not limited to, maleimide, N-methyl maleimide,N-cyclohexyl maleimide, N-phenyl maleimide and the like. These may beused either alone or in a mixture.

Meanwhile, the acrylic film may be a film including a(meth)acrylate-based resin having a lactone ring structure. Specificexamples of the (meth)acrylate-based resin having a lactone ringstructure include (meth)acrylate-based resins having a lactone ringstructure, which are described in, for example, the official gazettes ofJapanese Patent Application Laid-Open Nos. 2000-230016, 2001-151814, and2002-120326, and the like.

The method of manufacturing the acrylic film is not particularlylimited, and for example, the acrylic film may be manufactured bysufficiently mixing a (meth)acrylate-based resin, other polymers, anadditive and the like by any appropriate mixing method to manufacture athermoplastic resin composition, and then film-molding the resincomposition, or may also be manufactured by preparing the(meth)acrylate-based resin, other polymers, an additive and the like inseparate solutions, mixing the solutions to form a homogeneous mixturesolution, and then film-molding the mixture solution. In addition, theacrylic film may be an unstretched film, or a stretched film. Thestretched film may be a uniaxially stretched film or a biaxiallystretched film, and the biaxially stretched film may be a simultaneousbiaxially stretched film or a sequential biaxially stretched film.

Meanwhile, the polarizing plate of the present invention may furtherinclude a primer layer between the adhesive layer and the protectivefilm in order to further enhance adhesive strength. In this case, theprimer layer may be formed by a method of applying a coating solutionincluding a water-dispersible polymer resin, a water-dispersibleparticulate and water on a protective film by using a bar coatingmethod, a gravure coating method and the like, and drying the coatingsolution. The water-dispersible polymer resin may be, for example, awater-dispersible polyurethane-based resin, a water-dispersible acrylicresin, a water-dispersible polyester-based resin or a combinationthereof, and the like, and for the water-dispersible particulate, it ispossible to use an inorganic-based particulate such as silica, titania,alumina and zirconia, or an organic-based particulate composed of asilicone-based resin, a fluorine-based resin, a (meth)acrylic resin, acrosslinked polyvinyl alcohol and a melamine-based resin, or acombination thereof, but the particulate is not limited thereto.

Meanwhile, the polarizer and the protective film may be attached by amethod of applying an adhesive on the surface of the polarizer or theprotective film by using a roll coater, a gravure coater, a bar coater,a knife coater, or a capillary coater, and the like, and then heatingand paper-laminating the polarizer or the protective film by a laminatedpaper roll, or laminating paper by compressing the polarizer and theprotective film at normal temperature, a method of irradiating UV afterthe paper-lamination, or the like. Meanwhile, as the adhesive, variousadhesives for a polarizing plate used in the art, for example, apolyvinyl alcohol-based adhesive, a polyurethane-based adhesive, anacrylic adhesive, a cationic or radical adhesive and the like may beused without limitation.

1-4. Adhesion Layer

Meanwhile, the polarizing plate of the present invention may include anadhesion layer at the upper portion of the protective layer, ifnecessary, for attachment to an optical film such as a display devicepanel or a phase difference film.

In this case, the adhesion layer may be formed by using various gluingagents well known in the art, and the kind thereof is not particularlylimited. For example, the adhesion layer may be formed by using arubber-based gluing agent, an acrylic gluing agent, a silicone-basedgluing agent, a urethane-based gluing agent, a polyvinyl alcohol-basedgluing agent, a polyvinyl pyrrolidone-based gluing agent, a polyacrylamide-based gluing agent, a cellulose-based gluing agent, a vinyl alkylether-based gluing agent and the like. Among them, it is particularlypreferred that an acrylic gluing agent is used in consideration oftransparency, heat resistance and the like.

Meanwhile, the adhesion layer may be formed by a method of applying agluing agent at the upper portion of the protective layer, and may alsobe formed by a method of attaching an adhesion sheet, which ismanufactured by applying a gluing agent on a release sheet, and thendrying the gluing agent, at the upper portion of the protective layer.

2. Image Display Device

The aforementioned polarizing plate of the present invention may beusefully applied to an image display device such as a liquid crystaldisplay device. The image display device may be, for example, a liquidcrystal display device including a liquid crystal panel and polarizingplates each provided on both surfaces of the liquid crystal panel, andin this case, at least one of the polarizing plates may be thepolarizing plate according to the present invention. In this case, thekind of liquid crystal panel included in the liquid crystal displaydevice is not particularly limited. For example, it is possible to applyall the publicly known panels such as a passive matrix type panel suchas a twisted nematic (TN)-type, a super twisted nematic (STN)-type, aferroelectric (F)-type, or a polymer dispersed (PD)-type; an activematrix type panel such as a two terminal or three terminal; an in planeswitching (IPS) panel and a vertical alignment (VA) panel without beinglimited to the kind thereof. Furthermore, the kinds of otherconfigurations which constitute the liquid crystal display device, forexample, the kinds of upper and lower substrates (e.g., a color filtersubstrate, or an array substrate) and the like are not particularlylimited, and the configuration publicly known in the field may beadopted without limitation.

BEST MODE

Hereinafter, the present invention will be described in more detail withreference to specific Examples.

Preparation Example 1 Manufacture of Acrylic Protective Film

A raw material pellet was manufactured by supplying a resin composition,in which poly(N-cyclohexylmaleimide-co-methylmethacrylate), astyrene-maleic anhydride copolymer resin and a phenoxy-based resin wereuniformly mixed with each other at a weight ratio of 100:2.5:5, to a 240extruder in which a portion from a raw material hopper to the extruderwas substituted with nitrogen, and melting the mixed resin compositionat 250° C.

PKFE (Mw=60,000, Mn=16,000, Tg=95° C.) manufactured by InChemRez® Co.,Ltd., was used as the phenoxy-based resin, Dylaeck 332 with a content of85 wt % of styrene and 15 wt % of anhydrous maleic anhydride was used asthe styrene-maleic anhydride copolymer resin, and as thepoly(N-cyclohexylmaleimide-co-methylmethacrylate) resin, a resin with acontent of 6.5 wt % of N-cyclohexylmaleimide as a result of NMR analysiswas used.

The obtained raw material pellet was dried under vacuum, melted by theextruder at 260° C., allowed to pass through a coat hanger-type T-die,and allowed to pass through a chrome plating casting roll and a dryingroll and the like to manufacture a film having a thickness of 150 μm. Apilot stretching device was used to stretch the film at a ratio of 170%in the MD direction at 125° C. by using the difference between speeds ofthe rolls, thereby manufacturing an acrylic film.

After the acrylic film manufactured by the aforementioned process wassubjected to corona treatment, a primer composition, in which 20 partsby weight of an oxazoline crosslinking agent (Nippon Shokubai Co., Ltd.,WS700) was added to a primer composition with a solid content of 10 wt %that is prepared by diluting CK-PUD-F (Chokwang urethane dispersion)with pure water, was coated on one surface of the acrylic film with a #7bar, and then the acrylic film was stretched at a ratio of 190% in a TDdirection at 130° C. using a tenter, thereby finally manufacturing anacrylic protective film having a primer layer thickness of 400 nm.

Preparation Example 2 Preparation of Radical Curable Composition

(1) Radical Curable Composition A

Radical curable composition A for a polarizing plate was prepared byadding 3 parts by weight of a radical initiator Irgacure-819(manufactured by Ciba Specialty Chemicals Co., Ltd.) to 100 parts byweight of a resin composition prepared by adding 64.5 wt % of glycerylmonoacrylate (GLA), 16.1 wt % of hydroxyethyl acrylate (HEA), 16.1 wt %of dimethylol tricyclodecane diacrylate (DCPDA) and 3.3 wt % ofdi-(methacryloyloxy ethyl)phosphate.

(2) Radical Curable Composition B

Radical curable composition B for a polarizing plate was prepared byadding 3 parts by weight of a radical initiator Irgacure-819(manufactured by Ciba Specialty Chemicals Co., Ltd.) to 100 parts byweight of a resin composition prepared by adding 56.5 wt % of glycerylmonoacrylate (GLA), 24.2 wt % of hydroxyethyl acrylate (HEA), 16.1 wt %of dimethylol tricyclodecane diacrylate (DCPDA) and 3.2 wt % ofdi-(methacryloyloxy ethyl)phosphate.

(3) Radical Curable Composition C

Radical curable composition C for a polarizing plate was prepared byadding 3 parts by weight of a radical initiator Irgacure-819(manufactured by Ciba Specialty Chemicals Co., Ltd.) to 100 parts byweight of a resin composition prepared by adding 32.3 wt % of glycerylmonoacrylate (GLA), 32.3 wt % of glyceryl methacrylate (GLM), 16.1 wt %of hydroxyethyl acrylate (HEA), 16.1 wt % of dimethylol tricyclodecanediacrylate (DCPDA) and 3.2 wt % of di-(methacryloyloxy ethyl)phosphate.

(4) Radical Curable Composition D

Radical curable composition D for a polarizing plate was prepared byadding 3 parts by weight of a radical initiator Irgacure-819(manufactured by Ciba Specialty Chemicals Co., Ltd.) to 100 parts byweight of a resin composition prepared by adding 16.1 wt % of glycerylmonoacrylate (GLA), 48.4 wt % of glyceryl methacrylate (GLM), 16.1 wt %of hydroxyethyl acrylate (HEA), 16.1 wt % of dimethylol tricyclodecanediacrylate (DCPDA) and 3.3 wt % of di-(methacryloyloxy ethyl)phosphate.

(5) Radical Curable Composition E

Radical curable composition E for a polarizing plate was prepared byadding 3 parts by weight of a radical initiator Irgacure-819(manufactured by Ciba Specialty Chemicals Co., Ltd.) to 100 parts byweight of a resin composition prepared by adding 55.5 wt % of glycerylmonoacrylate (GLA), 13.9 wt % of hydroxyethyl acrylate (HEA), 27.8 wt %of dimethylol tricyclodecane diacrylate (DCPDA) and 2.8 wt % ofdi-(methacryloyloxy ethyl)phosphate.

(6) Radical Curable Composition F

Radical curable composition F for a polarizing plate was prepared byadding 3 parts by weight of a radical initiator Irgacure-819(manufactured by Ciba Specialty Chemicals Co., Ltd.) to 100 parts byweight of a resin composition prepared by adding 72.6 wt % of glycerylmonoacrylate (GLA), 8.1 wt % of hydroxyethyl acrylate (HEA), 16.1 wt %of dimethylol tricyclodecane diacrylate (DCPDA) and 3.2 wt % ofdi-(methacryloyloxy ethyl)phosphate.

(7) Radical Curable Composition G

Radical curable composition G for a polarizing plate was prepared byadding 3 parts by weight of a radical initiator Irgacure-819(manufactured by Ciba Specialty Chemicals Co., Ltd.) to 100 parts byweight of a resin composition prepared by adding 76 wt % of glycerylmonoacrylate (GLA), 19 wt % of hydroxyethyl acrylate (HEA) and 5 wt % ofdi-(methacryloyloxy ethyl)phosphate.

(8) Radical Curable Composition H

Radical curable composition H for a polarizing plate was prepared byadding 3 parts by weight of a radical initiator Irgacure-819(manufactured by Ciba Specialty Chemicals Co., Ltd.) to 100 parts byweight of a resin composition prepared by adding 66.7 wt % of glycerylmonoacrylate (GLA), 16.65 wt % of hydroxyethyl acrylate (HEA) and 16.65wt % of dimethylol tricyclodecane diacrylate (DCPDA).

(9) Radical Curable Composition I

Radical curable composition I for a polarizing plate was prepared byadding 3 parts by weight of a radical initiator Irgacure-819(manufactured by Ciba Specialty Chemicals Co., Ltd.) to 100 parts byweight of a resin composition prepared by adding 80.6 wt % ofhydroxyethyl acrylate (HEA), 16.1 wt % of dimethylol tricyclodecanediacrylate (DCPDA) and 3.3 wt % of tri-(acryloyloxy ethyl)phosphate.

Example 1

Radical curable composition A was applied on a primer layer of anacrylic film-based protective film prepared in Preparation Example 1 byusing a dropper, and lamination was performed on one surface of apolarizer (PVA device), a condition was set such that the thickness ofthe final adhesive layer became 1 to 2 μm, and then the film was allowedto pass through a laminator (5 m/min). Then, a polarizing plateincluding a protective film on one surface of a polarizer wasmanufactured by irradiating UV light with 1,000 mJ/cm² on a surface, onwhich the acrylic film was laminated, using a UV irradiation device(metal halide lamp).

Next, Radical curable composition A was applied on the other surface ofthe surface on which the protective film of the polarizer of thepolarizing plate manufactured above was laminated, a PET film having arelease force was laminated, a condition was set such that the thicknessof the final protective layer became 4 to 5 μm, and then the film wasallowed to pass through a laminator (5 m/min). Then, a polarizing plateincluding a protective film on one surface of a polarizer and aprotective layer on the other surface thereof was manufactured byirradiating UV light with 1,000 mJ/cm² on a surface, on which a releasePET film was laminated, using a UV irradiation device (metal halidelamp), and removing the PET film.

Example 2

A polarizing plate was manufactured in the same manner as in Example 1,except that Radical curable composition B was used.

Example 3

A polarizing plate was manufactured in the same manner as in Example 1,except that Radical curable composition C was used.

Example 4

A polarizing plate was manufactured in the same manner as in Example 1,except that Radical curable composition D was used.

Example 5

A polarizing plate was manufactured in the same manner as in Example 1,except that Radical curable composition E was used.

Example 6

A polarizing plate was manufactured in the same manner as in Example 1,except that Radical curable composition F was used.

Comparative Example 1

A polarizing plate was manufactured in the same manner as in Example 1,except that Radical curable composition G was used.

Comparative Example 2

A polarizing plate was manufactured in the same manner as in Example 1,except that Radical curable composition H was used.

Comparative Example 3

A polarizing plate was manufactured in the same manner as in Example 1,except that Radical curable composition I was used.

Experimental Example 1 Hydroxyl Value

The total hydroxyl values of the radical curable compositions used inthe Examples and the Comparative Examples were measured, and are shownin the following [Table 1]. In this case, the total hydroxyl value ofthe radical curable composition was calculated by using the followingEquation (1).

(molecular weight of KOH×number of —OH in a sample×1,000)/molecularweight of the sample  Equation (1):

Experimental Example 2 Evaluation of Adhesion

Adhesion of the protective layers of the polarizing plates manufacturedin the Examples and the Comparative Examples were measured, and areshown in the following [Table 1]. Specifically, the radical curablecompositions used in the Examples and the Comparative Examples wereapplied at a thickness of 4 to 5 μm on a polarizer (PVA device), apolarizer (PVA device) was laminated thereon and allowed to pass througha laminator, and then a UV irradiation device (metal halide lamp) wasused to irradiate UV rays thereon at 1,000 mJ/cm², thereby preparing apeel strength sample composed of a polarizer/a protective layer/apolarizer. The prepared sample was left to stand under conditions of atemperature of 20° C. and a humidity of 70% for 4 days, and then cutinto a width of 20 mm and a length of 100 mm, and a texture analyzerdevice (TA-XT Plus manufactured by Stable Micro Systems Ltd.) was usedto measure a peel strength at a speed of 300 m/min and an angle of 90degrees. In this case, the sample was indicated as excellent, good andbad when the peel strength thereof is 1.0 N/2 cm to 2.0 N/2 cm, 0.5 N/2cm or more and less than 1.0 N/2 cm, and less than 0.5 N/2 cm,respectively.

Experimental Example 3 Evaluation of Water Resistance

Water resistance of the polarizing plates manufactured in the Examplesand the Comparative Examples was measured, and is shown in the following[Table 1]. Specifically, the polarizing plates in the Examples and theComparative Examples were laminated on a glass substrate, and thenimmersed in a thermostat at 60° C., and the water resistance was judgedby observing whether the end portions of the polarizing plate had beendiscolored after 8 hours, and the cases in which no change was observedand discoloration occurred were indicated as excellent and bad,respectively.

TABLE 1 Hydroxyl value Water Classification Composition [mgKOH/g]Adhesion resistance Example 1 A 591 Excellent Excellent Example 2 B 568Excellent Excellent Example 3 C 569 Excellent Excellent Example 4 D 558Excellent Excellent Example 5 E 508 Excellent Excellent Example 6 F 614Excellent Excellent Comparative G 702 Excellent Bad Example 1Comparative H 593 Good Bad Example 2 Comparative I 389 Bad Bad Example 3

As can be seen in Table 1, it can be known that in Examples 1 to 6 ofthe present invention, adhesion was excellent, and water resistance wasalso excellent.

In contrast, it can be known that in the case of Comparative Example 1in which (B) the compound was not included, water resistance wasreduced, and likewise, in the case of Comparative Example 2, waterresistance was also reduced.

Further, it can be known that in the case of Comparative Example 3 inwhich a phosphate compound having three acryloyl group was used as (C)the compound, both adhesive strength and water resistance were bad.

Meanwhile, in the case of the Examples, the adhesive layer and theprotective layer were manufactured by using the same radical curablecomposition for convenience when the polarizing plate was manufactured,but the present invention is not limited thereto.

As described above, exemplary embodiments of the present invention havebeen described in detail, but it will be obvious to a person withordinary skill in the art that the scope of the present invention is notlimited thereto, and various modifications and changes may be madewithout departing from the technical spirit of the present inventiondescribed in the claims.

1. A polarizing plate comprising: a polarizer; and a protective layerformed on at least one surface of the polarizer, wherein the protectivelayer is a cured product of a radical curable composition including: (A)a radical polymerizable compound including at least one hydrophilicfunctional group in a molecule thereof; (B) a multifunctional(meth)acrylic compound; and (C) a phosphate compound including one ortwo (meth)acryl group in a molecule thereof; and (D) a radicalinitiator.
 2. The polarizing plate of claim 1, wherein the radicalcurable composition comprises more than 30 parts by weight and 93 partsby weight or less of (A) the radical polymerizable compound having atleast one hydrophilic functional group in a molecule thereof; 5 to 40parts by weight of (B) the multifunctional (meth)acrylic compound; 1 to40 parts by weight of (C) the phosphate compound including one or two(meth)acryl groups in a molecule thereof; and (D) 0.5 to 20 parts byweight of the radical initiator, based on 100 parts by weight of theradical curable composition.
 3. The polarizing plate of claim 1, whereinthe radical curable composition has a total hydroxyl value of 500 to 900mg KOH/g.
 4. The polarizing plate of claim 1, wherein the hydrophilicfunctional group of (A) the radical polymerizable compound is a hydroxygroup.
 5. The polarizing plate of claim 4, wherein (A) the radicalpolymerizable compound is a mixture of (a-1) a radical polymerizablecompound having one hydroxy group in a molecule thereof and (a-2) aradical polymerizable compound having at least two hydroxy groups in amolecule thereof.
 6. The polarizing plate of claim 1, wherein (B) themultifunctional (meth)acrylic compound comprises one or more selectedfrom the group consisting of compounds represented by the following[Formula I] to [Formula III]:

in [Formula I], R₁ and R₂ are each independently a (meth)acryloyloxygroup or a (meth)acryloyloxy alkyl group.

in [Formula II], R₃, R₄ and R₅ are each independently a(meth)acryloyloxy group, or a (meth)acryloyloxy alkyl group, and R₆ is a(meth)acryloyloxy group, a (meth)acryloyloxy alkyl group, a hydroxygroup, or a substituted or unsubstituted C_(1˜10) alkyl group.

in [Formula III], R₇ is a substituted or unsubstituted C_(1˜10)alkylene, and R₈ and R₉ are each independently a (meth)acryloyloxy groupor a (meth)acryloyloxy alkyl group.
 7. The polarizing plate of claim 1,wherein (C) the phosphate compound comprises a compound represented bythe following [Formula IV]:

in [Formula IV], R₁₀ is a substituted or unsubstituted C_(1˜10) alkylenegroup, a substituted or unsubstituted C_(4˜14) cycloalkylene group, asubstituted or unsubstituted C_(6˜14) arylene group, or a combinationthereof; R₁₁ is hydrogen or a methyl group; and n is an integer of 1 and2, m is an integer of 1 and 2, and n+m=3.
 8. The polarizing plate ofclaim 1, wherein the protective layer has a thickness of 0.5 to 20 μm.9. The polarizing plate of claim 1, wherein a protective film isattached to a surface opposite to a surface of the polarizer, on whichthe protective layer is formed, through an adhesive layer.
 10. Thepolarizing plate of claim 1, further comprising: an adhesion layer at anupper portion of the protective layer.
 11. An image display devicecomprising the polarizing plate of claim 1.